Highly Tunable Piezoelectricity of Flexible Nanogenerators Based on 3D Porously Architectured Membranes for Versatile Energy Harvesting and Self-Powered Multistimulus Sensing

The development of inherently flexible nano-generators that can effectively convert various environmental resources (pressure, magnetism, solvents, etc.) into electricity is highly desirable for developing sustainable energy. Herein, we demonstrate a flexible piezoelectric nanogenerator with highly tunable piezoelectricity, high sensitivity, and multistimulus sensing capability based on the 3D porous architecture of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nano-composite membrane featured by interconnected network-interfaced magnetic Fe3O4 nanoparticles. Fe3O4 nanoparticles are incorporated to endow the nanogenerator with responsiveness to magnetism. The porous membrane is fabricated by a scalable, template-free, nonsolvent-induced phase-separation approach. By modulating the liquid-liquid demixing separation and nanoparticle migration, pore sizes of the spongy network are effectively tuned over a wide range, by which the porosity, flexibility, and electroactive crystal growth are significantly enhanced. Consequently, the device produces an enhanced piezoelectricity with a superior piezoelectric coefficient d(33) of 48.6 pC/N, a sensitivity of 294 mV/N, a power density of 5.3 mu W/cm(3), and stable electricity-generating performance over 10,000 repetitions. Significant enhancements over the pristine nonporous control are attributed to the facilitated structural deformation, localized stress concentration, and the electroactive crystal promotion. More intriguingly, beyond the response to the contact pressure, the nanogenerator can also yield continuous electric power in response to the magnetic field and organic solvent vapor due to the actuation-driven piezoelectric effects. The versatile nanogenerator with multiple responsiveness permits the self-powered smart sensing of various ambient stimuli and the simultaneous harvesting of the associated energies in both contact and noncontact working modes. This study demonstrates the substantial potential of multistimulus-responsive, porously architectured membrane-based piezoelectric nanogenerators in multifunctional, contactless, and efficient energy harvesting and sensing for wearable and portable electronics.